TITLE: GCN CIRCULAR NUMBER: 17480 SUBJECT: GRB 150219A: Swift-XRT afterglow detection DATE: 15/02/19 23:34:23 GMT FROM: Valerio D'Elia at ASDC K.L. Page (U. Leicester), C. Pagani (U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the INTEGRAL-detected burst GRB 150219A (Mereghetti et al. GCN Circ. 17476), collecting 2.6 ks of Photon Counting (PC) mode data between T0+10.5 ks and T0+23.4 ks. An uncatalogued X-ray source is detected inside the INTEGRAL error region and is fading with 3-sigma significance, and is therefore likely the GRB afterglow. The position of this source is RA, Dec=271.2507, -41.5942 which is equivalent to: RA (J2000): 18:05:0.18 Dec(J2000): -41:35:39.0 with an uncertainty of 3.7 arcsec (radius, 90% confidence). This position is 53 arcsec from the INTEGRAL position. The light curve can be modelled with a power-law decay with a decay index of alpha=2.8 (+0.9, -0.7). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.8 (+/-0.4). The best-fitting absorption column is 1.6 (+0.6, -0.5) x 10^22 cm^-2, in excess of the Galactic value of 1.4 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.3 x 10^-11 (1.1 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.6 (+0.6, -0.5) x 10^22 cm^-2 Galactic foreground: 1.4 x 10^21 cm^-2 Excess significance: 4.6 sigma Photon index: 1.8 (+/-0.4) If the light curve continues to decay with a power-law decay index of 2.8, the count rate at T+24 hours will be 5.8 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.6 x 10^-14 (6.2 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis of the likely afterglow are at http://www.swift.ac.uk/ToO_GRBs/00020483/index_1.php. The results of the full analysis of the XRT observations are available at http://www.swift.ac.uk/ToO_GRBs/00020483. This circular is an official product of the Swift-XRT team.